1. Field of the Invention
The present invention relates to a method of processing image signal. More particularly, the present invention relates to a device and method for sharpening an image signal.
2. Description of the Related Art
Due to factors such as limited bandwidth or inferior image processing treatment in the current signal transmission standard or image signal processing scheme, the image object often has blurry edges or insufficiently sharpened demarcation lines. To improve the quality of the received images or to enhance the contrast of the received images, a technique capable of enhancing the transient at the edge of an image object has been developed so that the image object is able to have a sharper boundary.
One important factor for increasing the sharpness of an image is to enhance the contrast such as luma or chroma on each side of the edge of an image object. However, the enhancing method must follow certain conditions, or else some other problems will arise. For example, the luma or chroma signal after enhancement must maintain the relative position of the original image signal. Furthermore, the signal amplitude must not overshoot or undershoot when compared with the original image signal amplitude. Obviously, an acceptable quality level must be maintained after the image is enhanced.
In U.S. Pat. No. 5,936,682, a method of sharpening the image is disclosed. Because a finite impulse response (FIR) filter is used, the amplitude of the enhanced image sometimes overshoots as well as undershoots. To eliminate the overshoot or undershoot of the amplitude of the enhanced image, additional circuitry is required to process the signal. Ultimately, sharpening the image will incur additional cost.